1. Field of the Invention
The invention relates to an audio system comprising an input for receiving an audio signal and an output for supplying an output signal, processing means for processing the received audio signal, and enhancing means, whereby the enhancing means comprises selecting means for selecting a part of the audio signal, and an harmonics generator for generating harmonics of the selected part of the audio signal.
The invention further relates to means for enhancing the perceived low frequency response in an audio system.
2. Description of the Related Art
High fidelity reproduction of audio signals ideally requires sound transducers capable of reliably reproducing sound throughout the listening range of human beings. This has been determined to be 20-20,000 Hz. However, realistically, most high fidelity speaker systems are capable of reproducing sounds in the frequency range of 40-20,000 Hz. These high fidelity systems include small transducers (tweeters) for reproducing the high end of the frequency range, and relatively large transducers (woofers) for reproducing the low end of the frequency range. Naturally these speaker systems are large in size and take up a substantial amount of space in the listening area.
However, there are many customers who enjoy high fidelity sound but do not have the space for a high fidelity speaker system. Manufacturers recognizing this problem have been marketing compact audio systems with small speaker systems for these consumers. However, in view of the relatively small size of the speaker systems, these small speaker systems are not capable of reproducing audio frequencies in the range of 40-100 Hz. The consumer using these compact audio systems is then able to notice this deficiency and is then disappointed with the system.
Such an audio system is known from the European patent application EP-A0546619 (applicants reference PHA40624). Since the invention of the electrodynamics loudspeaker, there is a need for greater acoustical output, especially at low frequencies. Often however, for instance in television sets or portable audio sets, this acoustical output is severely limited by the small size of the loudspeakers. It is known that this dilemma can be solved by using a psycho-acoustic phenomenon often referred to as virtual pitch or missing fundamental, which evokes the illusion of a higher bass-response, while the loudspeaker does not radiate more power at these low frequencies. This illusion can be created by replacing low-frequency tones, which are present in the audio signal but can not be reproduced by a small loudspeaker, by harmonics of these tones. The harmonics now represent the low-frequency tones, the so-called ultra bass.
In the known audio system a low-frequency band of an audio signal is selected and supplied to enhancing means, in the form of a harmonics generator for generating harmonics of the selected signal. The generated harmonics are thereafter added to the audio signal. In this way, the low-frequency perception of the audio signal is improved. In the known audio system, a full wave rectifier is used as harmonics generator, which generates only even harmonics.